The objective of the proposed research is to study induced conformations resulting from peptide/lipid and peptide/peptide interactions. This will be accomplished by studying the perturbations of induced conformations using reversed-phase high-performance liquid chromatography (RP-HPLC) in conjunction with circular dichroism (CD). An essential element in our approach involves the systematic design and synthesis of complete series of related peptides in which only one variable in the starting parent sequence will be altered at a given time (i.e. , a single amino acid omitted, inserted, substituted, etc.) . The results for all of the peptides studied will be then correlated with their biological activities, such as antimicrobial activity, and/or red blood cell lysis. The dominant causative factor responsible for the biological activity of peptides is believed to be their induced secondary structures at their specific sites of action. Although peptides virtually always exert their functional activity at biological interfaces, the specific secondary structures into which they are induced at such interfaces cannot be readily determined. Technological improvements in NMR and X-ray crystallography enable conformational studies of this kind to be carried out, but these technologies are time-consuming and limited to those laboratories with the required physical and computing facilities. Therefore, we will study the relative induced secondary structures of specific peptide series as determined by variation of their RP-HPLC retention times. In this way, we expect to be able to assess the potential general usefulness of RP-HPLC as a system modeling biologically relevant aqueous/lipid interfaces. The simplicity and availability of RP-HPLC will enable the majority of laboratories to take advantage of our current and future results. As a complementary approach, synthetic combinatorial peptide libraries, comprised of tens of millions of peptides, will be used to study melittin's sites of interaction with red blood cell membranes. These approaches are expected to have a significant impact on the understanding of peptide interactions in the fields of immunology, molecular biology, and microbiology.